A known occupant detection method is suggested in which seating of an occupant at a seat of a vehicle is detected and a physical build of the occupant is estimated. For example, when an occupant becomes seated at a seat, an occupant detection apparatus described in JP2003-329507A (which will be hereinafter referred to as Patent reference 1) monitors a transition of a seat load that changes with time. The known occupant detection apparatus is configured to estimate a physical build of the occupant by comparing the seat load with first and second threshold values.
That is, when the occupant is getting seated at the seat, a detection value of the seat load is increased due to that the occupant becomes seated onto a seat cushion. Then, the detection value comes to be stabilized at a lower value than the highest value in an increasing process of the detection value, that is, a local maximum in the increasing process of the detection value.
In view of the above-described aspect, the known occupant detection apparatus determines whether or not the detection value of the seat load exceeds the second threshold value that is larger than the first threshold value, after the detection value of the seat load exceeds the first threshold value (refer to FIG. 15 of Patent reference 1) due to the seating of the occupant onto the seat. In a case where the detection value of the seat load does not reach the second threshold value within a predetermined time period, it is determined that the occupant is in a region of a light load, that is, weight of the occupant is light.
In addition, the known technique determines that the occupant is in a region of a heavy load, that is, the weight of the occupant is heavy, in a case where the detection value of the seat load does not fall below the second threshold value within a predetermined time period after the detection value of the seat load exceeds the second threshold value. On the basis of the weight of the occupant that is estimated from the above-explained determination, it is decided whether or not an airbag mounted on the vehicle is to be inflated or not to be inflated, or a working pressure of the airbag is chosen.
Recently, however, a seating state of an occupant at a seat is considered not only in the airbag inflation control but also in various fields of control at a vehicle. Thus, a higher accuracy is required in the estimation of the physical build of the occupant.
That is, in the above-explained known technique, the build of the occupant is estimated to be large in a case where the weight of the occupant is heavy and the build of the occupant is estimated to be small in a case where the weight of the occupant is light. However, a physical build of an occupant whose body height is tall and a physical build of an occupant whose body height is short may differ largely from each other even when the weights of the occupants are the same. Accordingly, there arises a problem that it is difficult to perform the most appropriate airbag inflation control, for example. In this aspect, there remains room for improvement.
A need thus exists for an occupant detection method and an occupant detection apparatus, which are not susceptible to the drawback mentioned above.